In general, a heat pump system means an air-conditioning system configured to perform cooling and heating at the same time using a single refrigerant system. The heat pump system includes a compressor, an indoor heat exchanger, an outdoor heat exchanger, an expansion valve, and a direction control valve.
In the heat pump system, when cooling is performed, a refrigerant is circulated along the paths of the compressor, the outdoor heat exchanger, the expansion valve, the indoor heat exchanger, and the compressor. When heating is performed, a refrigerant is circulated along the paths of the compressor, the indoor heat exchanger, the expansion valve, the outdoor heat exchanger, and the compressor.
That is, when cooling is performed, the indoor heat exchanger operates as an evaporator and the outdoor heat exchanger operates as a condenser. When heating is performed, the indoor heat exchanger operates as a condenser and the outdoor heat exchanger operates as an evaporator.
FIG. 1 is a configuration illustrating a conventional heat pump system for a vehicle, which is disclosed in Korean Patent Application Publication No. 10-2008-0026983. The conventional heat pump system for a vehicle includes a compressor 10 and an indoor heat exchanger 20. The compressor 10 compresses an evaporated refrigerant into gas of a high temperature and high pressure. The indoor heat exchanger 20 performs heat exchange of a compressed refrigerant of a high temperature and high pressure with external air.
The conventional heat pump system for a vehicle includes an expansion valve 30, an outdoor heat exchanger 40, and an internal heat exchanger 50. The expansion valve 30 expands a refrigerant that has been subjected to a heat exchange by the indoor heat exchanger 20 at a low temperature and low pressure. The outdoor heat exchanger 40 receives the expanded refrigerant of a low temperature and low pressure and evaporates the received refrigerant by performing heat exchange of the received refrigerant ambient air. In particular, the outdoor heat exchanger 40 is installed outside a vehicle and is configured to evaporate the refrigerant of a low temperature and low pressure while absorbing surrounding heat.
The internal heat exchanger 50 performs heat exchange of a refrigerant on the outlet side of the indoor heat exchanger 20 with a refrigerant on the outlet side of the outdoor heat exchanger 40 and forcibly lowers a temperature of a refrigerant on the outlet side of the indoor heat exchanger 20.
The internal heat exchanger 50 is equipped with a first passage 52 and a second passage 54 corresponding to each other. A refrigerant of a high temperature that flows from the indoor heat exchanger 20 to the expansion valve 30 may pass through the first passage 52. A refrigerant of a low temperature that flows from the outdoor heat exchanger 40 to the compressor 10 may pass through the second passage 54. The refrigerant of a high temperature that passes through the first passage 52 and the refrigerant of a low temperature that passes through the second passage 54 are subjected to mutual heat exchange.
In this case, the conventional heat pump system includes heating means 60 for heating a refrigerant that flows from the second passage 54 of the internal heat exchanger 50 to the compressor 10. The heating means 60 may be formed of a hot wire or Positive Temperature Coefficient (PTC) heater 62.
Such conventional heat pump system for a vehicle includes control logic for forcibly cutting off an electromotive compressor in order to prevent overload of a system when cooling or heating is performed.
When cooling is performed (i.e., in air-conditioning mode), if discharge pressure, that is, pressure on the high pressure side, exceeds a specific level while the electromotive compressor operates, the electromotive compressor is forcibly cut off for the durability and safety of the heat pump system.
Furthermore, when heating is performed (i.e., in heat pump mode), the electromotive compressor may be cut off due to an overcurrent that is attributable to an increased load even in the same number of rotations per minute (rpm) of the compressor because a compression ratio of a refrigerant is increased compared to a case where cooling is performed due to a low outside temperature.
If the electromotive compressor is unexpectedly cut off when cooling is performed or when heating is performed as described above, a passenger in a vehicle may feel uncomfortable because the electromotive compressor does not perform cooling and heating inside the vehicle. Furthermore, there is a problem in that noise and vibration are generated due to repeated restarts.